Case Report Monoclonal IgG1k Anti–Glomerular Basement Membrane Disease: A Case Report Shana M. Coley, MD, PhD,1 Shayan Shirazian, MD,2 Jai Radhakrishnan, MD,3 and Vivette D. D’Agati, MD1 We report a case of anti–glomerular basement membrane (anti-GBM) nephritis with indolent course, monoclonal IgG1k (immunoglobulin G, subclass 1, k light chain) linear staining of the GBM, and multifocal GBM breaks but without crescents or detectable serum anti-GBM antibody in a patient followed over 9 years. Atypically, anti-GBM nephritis follows an indolent course. A very small fraction of patients with anti-GBM nephritis lack detectable circulating anti-GBM antibodies, and rare reports of monoclonal anti-GBM nephritis exist. We report what is to our knowledge the first case manifesting all 3 of these rare variations. Our patient initially presented with asymptomatic decreased kidney function following an upper respiratory tract infection. He was found to have microhematuria and subnephrotic proteinuria with mild diffuse endocapillary proliferative and exudative glomerulonephritis with linear IgG1k staining of the GBM. He was treated with an induction regimen of intravenous cyclophosphamide and corticosteroids followed by maintenance monotherapy with mycophenolic acid. Nine years later, repeat kidney biopsy for worsening kidney function after an upper respiratory tract infection showed persistent monoclonal staining of the GBM and acute glomerulonephritis with increased chronicity, including a single fibrocellular crescent. Despite extensive clinical investigations spanning nearly a decade, no circulating anti-GBM antibody or monoclonal protein has been detected. In this case report, we explore the unique features of this monoclonal IgG1k-associated anti-GBM nephritis. Am J Kidney Dis. 65(2):322-326. ª 2015 by the National Kidney Foundation, Inc. INDEX WORDS: Glomerular basement membrane (GBM); anti-GBM nephritis; anti-GBM disease; Goodpasture syndrome; monoclonal autoantibody; IgG1k; glomerulonephritis; kidney biopsy.
A
nti–glomerular basement membrane (anti-GBM) disease (also known as Goodpasture syndrome) is an autoimmune disorder that typically presents as pulmonary hemorrhage and rapidly progressive glomerulonephritis. However, milder renal-limited forms of the disease occur.1 The disease is triggered by autoantibodies directed against the “Goodpasture antigen,” the noncollagenous (NC1) domain of the a3 chain of type IV collagen expressed on basement membranes of glomerular and pulmonary capillaries.2,3 Circulating antibodies with specificity for GBM proteins are pathognomonic and detected in more than 97% of patients with anti-GBM disease.4,5 These autoantibodies almost always are polyclonal immunoglobulin G (IgG), with rare reported cases of polyclonal IgA-mediated or monoclonal From the 1Department of Pathology & Cell Biology, Columbia University Medical Center, New York, NY; 2Winthrop University Hospital, Mineola, NY; and 3Department of Medicine, Columbia University Medical Center, New York, NY. Received May 20, 2014. Accepted in revised form August 6, 2014. Originally published online October 21, 2014. Address correspondence to Vivette D. D’Agati, MD, Department of Pathology, Columbia University, College of Physicians and Surgeons, Renal Pathology Laboratory, Rm VC14-224, 630 W 168th St, New York, NY 10032. E-mail: [email protected] 2015 by the National Kidney Foundation, Inc. 0272-6386 http://dx.doi.org/10.1053/j.ajkd.2014.08.022 322
gammopathy–associated anti-GBM disease.6-8 In kidney biopsy specimens, smooth linear staining for IgG is seen exclusively along the GBM, and the most common histologic pattern is severe necrotizing and crescentic glomerulonephritis.9 Treatment involves cyclophosphamide, high-dose corticosteroids, and/or plasmapheresis.10 The prognosis of untreated anti-GBM disease is poor, and kidney survival correlates with the percentage of glomeruli containing crescents.9,10 We report a patient with monoclonal anti-GBM antibody–related glomerulonephritis without a circulating antibody who showed an indolent clinical course.
CASE REPORT A 53-year-old white man was referred to nephrology after developing asymptomatic decreased kidney function following a viral upper respiratory tract infection 4 months prior. He had a history of hypertension and atypical angina and had been taking a statin and verapamil for the 3 years leading up to presentation. He denied hemoptysis, skin rash, or joint pain. Physical examination was unremarkable. Laboratory studies showed the following values: serum creatinine (Scr), 3 mg/dL (corresponding to estimated glomerular filtration rate [eGFR] of 22 mL/min/1.73 m2, as calculated using the isotope-dilution mass spectrometry–traceable 4-variable MDRD [Modification of Diet in Renal Disease] Study equation); albumin, 4.5 g/dL; hemoglobin, 9.9 mg/dL; white blood cell count, 7.8 3 103/mL; and platelet count, 274 3 103/mL. Urine studies revealed microhematuria, and urine protein-creatinine ratio was 689 mg/g. Serologic tests were negative for antinuclear antibody, antineutrophil cytoplasmic antibody, anti-GBM antibody, Am J Kidney Dis. 2015;65(2):322-326
Monoclonal IgG1k anti-GBM Disease
Figure 1. Histologic findings in the initial biopsy and 9-year follow-up biopsy specimens. Light microscopy of the initial kidney biopsy specimen showed (A) diffuse endocapillary proliferative and exudative glomerulonephritis with (B) multifocal GBM breaks (arrows), (C) many glomerular monocytes/macrophages, and (D) focal red blood cell casts. Follow-up kidney biopsy 9 years later also showed (E) diffuse endocapillary proliferative and exudative glomerulonephritis, though now (F) with a single fibrocellular crescent, and (G) severe global glomerulosclerosis and moderate tubulointerstitial scarring. Immunofluorescence micrographs showing monoclonal IgG1k (immunoglobulin G, subclass 1, k light chain) linear staining of glomerular basement membranes ([H] IgG1; [I] IgG2; [J] IgG3; [K] IgG4; [L] k light chain; [M] l light chain). (A, D, E) Hematoxylin and eosin stain, (B, F, G) Jones methenamine silver stain, (C) CD68 immunostain. Original magnification, 3600, except for panel G (3200).
antistreptolysin O antibody, anti–hepatitis B virus, and anti–hepatitis C virus antibodies. There was no hypocomplementemia. Kidney biopsy (Fig 1A-D) showed mild diffuse endocapillary proliferative and exudative glomerulonephritis with many intracapillary monocytes/macrophages and multifocal GBM breaks, focal red blood cell casts, moderate interstitial inflammation and edema, and mild tubulointerstitial scarring. Immunofluorescence microscopy (Fig 1H-M) revealed intense diffuse linear staining of the GBM for IgG and k light chain, with sparse granular staining (trace to 11) of glomerular capillary walls for C3 and no detectable staining for IgM, IgA, C1, and l light chain (Dako). There was no staining detected in Bowman capsule, tubular basement membranes, or vessel walls. Staining for the IgG subclasses (antibodies obtained from The Binding Site) showed restricted positivity for IgG1 with no detectable positivity for IgG2, IgG3 or IgG4 along the GBM (Fig 1H-K). Electron microscopy detected multifocal gaps in the GBM and no electron-dense deposits (Fig 2). Curiously, no crescents or fibrinoid necrosis were seen in more than 20 glomeruli sampled. Following biopsy, serum and urine protein electrophoresis with immunofixation were negative for monoclonal protein. Repeat serologic test results for anti-GBM antibody, antineutrophil cytoplasmic antibody, antinuclear antibody, antistreptolysin O antibody, anti-hepatitis B virus antibody, anti-hepatitis C virus antibody, C3, and C4 were negative or normal. Prednisone (80 mg/d) was given, then the dosage was tapered over 2 months, Am J Kidney Dis. 2015;65(2):322-326
after which the patient’s Scr level peaked at 4 mg/dL (eGFR, 16 mL/min/1.73 m2). Repeat kidney biopsy showed similar histologic findings, and the patient was treated with a 6-month course of intravenous cyclophosphamide (750 mg/m2) and oral prednisone (60 mg/d) and then switched to maintenance monotherapy with mycophenolic acid (720 mg twice daily). He did well for many years, with stable Scr levels of w1.7 mg/dL (eGFR, 42 mL/ min/1.73 m2) and persistent microhematuria and proteinuria (protein excretion quantified at 0.4-1.5 g/d). Because multiple commercially available tests had failed to detect circulating anti-GBM antibody, indirect immunofluorescence was performed by layering the patient’s serum on normal kidney tissue. Again, no anti-GBM antibody was detected, though the false-negative rate for this technique can reach 40%.11 Myeloma workup was negative, including positron emission tomography-computed tomography and bone marrow biopsy. Results from multiple serum free light chain studies showed normal levels of k and l light chains with k:l ratio ranging from 1.11 to 1.82, at times mildly elevated according to the reference range (0.26-1.65). However, the ratio remained within the expected range for patients with decreased kidney function (0.373.1).12 Cryoglobulin studies and serum protein electrophoresis results were repeatedly negative. Nine years after the original episode, the patient again presented with worsening kidney function (Scr, 2.15 mg/dL; eGFR, 31 mL/ min/1.73 m2), proteinuria with protein excretion of 910 mg/d, 323
Coley et al
Figure 2. Electron micrographs show (A) representative gap in glomerular basement membranes plugged by apposition of endothelial cells and podocytes (arrows, initial biopsy; original magnification, 325,000). No immune-type electron-dense deposits were seen in the (B) initial kidney biopsy (original magnification, 350,000) or (C) 9-year follow-up biopsy specimen (original magnification, 310,000).
and hematuria (21 red blood cells/high-power field) after a viral upper respiratory tract infection. The kidney biopsy specimen showed mild diffuse endocapillary proliferative and exudative glomerulonephritis, though this time with a single fibrocellular crescent, severe global glomerulosclerosis, and moderate tubulointerstitial scarring (Fig 1E-G). Again, strong smooth linear and IgG1k (IgG subclass 1, k light chain)–restricted staining of the GBM highlighted focal GBM breaks; no electron-dense deposits were seen (Fig 2C). Repeat testing for anti-GBM antibody (multiplex bead assay) gave negative results. He was treated with 2 doses of rituximab (1 g) separated by 2 weeks. At the time of writing this article, the patient’s Scr level was 1.9 mg/dL (eGFR, 36 mL/min/1.73 m2), urine protein-creatinine ratio was 1.70 mg/g, and urinalysis showed 13 red blood cells/high-power field. He remains on treatment with mycophenolic acid, 720 mg twice daily. Overall, our patient experienced a relatively indolent course of kidney disease punctuated by episodes of increased clinical activity. Kidney biopsy showed some features of anti-GBM nephritis, including linear staining along the GBM and breaks in the GBM, but unusual features of monoclonal staining and mild endocapillary proliferation without fibrinoid necrosis or crescents, except for a single fibrocellular crescent only in the most recent biopsy specimen. Over a 9-year span, glomerulosclerosis and tubulointerstitial scarring increased from 5% to 70% and 10% to 40%, respectively, despite ongoing immunosuppressive therapy.
DISCUSSION Considering the strong monoclonal IgG staining of GBM, the histologic differential diagnosis includes atypical anti-GBM nephritis, light and heavy chain immunoglobulin deposition disease, and proliferative glomerulonephritis with monoclonal immunoglobulin deposits. The absence of linear staining of tubular basement membranes and absence of nodular 324
glomerulosclerosis provided evidence against light and heavy chain immunoglobulin deposition disease.13 Although the monoclonal IgG deposits in proliferative glomerulonephritis with monoclonal immunoglobulin deposits are limited to glomeruli, the absence of glomerular electron-dense deposits ruled out this possibility.14 By exclusion, atypical anti-GBM nephritis was supported by the GBM-restricted linear IgG deposits and multifocal ruptures of the GBM without corresponding electron-dense deposits. Atypical features included the mild endocapillary proliferative pattern without fibrinoid necrosis or crescents, monoclonal nature of the IgG staining, indolent course, and undetectable GBMspecific antibody in the circulation. Passive adsorption of IgG resulting in linear GBM staining without electrondense deposits can be seen with diabetes or monoclonal paraproteinemia, neither of which was detected in our patient. Although we cannot definitively exclude passive adsorption without a positive test for GBM-specific antibody, we believe the atypical findings fit best with a monoclonal form of anti-GBM nephritis. Typically, anti-GBM disease manifests as polyclonal IgG bound to GBM, with studies showing variable results regarding the dominant IgG subtype.4,15,16 Other case reports of monoclonal antibody–associated anti-GBM disease have involved IgA, IgM, or l light chain only.17-19 Our case is the first report of anti-GBM disease with linear GBM staining for monoclonal IgG. Typical screening tests for circulating anti-GBM antibody are based on enzyme-linked immunosorbent Am J Kidney Dis. 2015;65(2):322-326
Monoclonal IgG1k anti-GBM Disease
assay (ELISA) using purified GBM proteins or recombinant Goodpasture antigen, which has reported sensitivity of 65% to 100%.5,20 False-negative results from ELISA testing have been attributed to anti-GBM antibody of low titer or directed toward nonGoodpasture GBM antigens.21,22 Of note, in 3 patients with crescentic anti-GBM disease and negative ELISA results for anti-GBM antibody, a biosensorbased assay was able to detect serum anti-GBM antibody of either low titer and/or low antigen-binding affinity.22 In several reports showing strong linear staining of the GBM but undetectable circulating antiGBM antibody, subsequent alternative serum assays detected an IgG4-predominant polyclonal anti-GBM antibody. This IgG4 predominance often was associated with milder kidney disease.23-26 Low-titer anti-GBM antibody and atypical autoantibody specificity also have been linked with less aggressive disease.27,28 A handful of cases of very mild kidney disease but strong linear GBM staining have been reported.23,26,29,30 Interestingly, one of these cases was associated with an IgG4-predominant autoantibody specific for a quaternary-structure epitope of the NC1 hexamer of a3, a4, and a5 chains of collagen IV and thus could not be detected using tests based on monomeric Goodpasture antigen.26 Our patient likely has a circulating monoclonal IgG1k anti-GBM antibody that we have not yet been able to detect. This antibody may be low titer, have a low rate of synthesis or a high rate of clearance, have low binding affinity, or be directed toward an atypical GBM epitope, explaining the negative results with commercially available screening tests. Alternately, our patient’s monoclonal anti-GBM antibody may be directed toward a private epitope (ie, an epitope unique to his GBM), which would explain the negative results by indirect immunofluorescence staining using his serum on normal kidney tissue. The reason that our patient’s disease course has been relatively indolent compared to the typical rapidly progressive course of anti-GBM disease may be because his monoclonal anti-GBM antibody inefficiently triggers downstream events that mediate the classic necrotizing and crescentic glomerulonephritis such as complement activation or neutrophil participation.11 In summary, we report a unique case of indolent anti-GBM nephritis associated with strong linear monoclonal IgG1k staining of the GBM and to date, no detectable circulating anti-GBM antibody or monoclonal paraprotein.
ACKNOWLEDGEMENTS Support: Dr Coley received fellowship funding supported by the Glomerular Center of Columbia University. Financial Disclosure: The authors declare that they have no relevant financial interests. Am J Kidney Dis. 2015;65(2):322-326
REFERENCES 1. Hudson BG, Tryggvason K, Sundaramoorthy M, Neilson EG. Alport’s syndrome, Goodpasture’s syndrome, and type IV collagen. N Engl J Med. 2003;348(25):2543-2556. 2. Pedchenko V, Bondar O, Fogo AB, et al. Molecular architecture of the Goodpasture autoantigen in anti-GBM nephritis. N Engl J Med. 2010;363(4):343-354. 3. Kalluri R, Wilson CB, Weber M, et al. Identification of the alpha 3 chain of type IV collagen as the common autoantigen in antibasement membrane disease and Goodpasture syndrome. J Am Soc Nephrol. 1995;6(4):1178-1185. 4. Segelmark M, Butkowski R, Wieslander J. Antigen restriction and IgG subclasses among anti-GBM autoantibodies. Nephrol Dial Transplant. 1990;5(12):991-996. 5. Sinico RA, Radice A, Corace C, Sabadini E, Bollini B. Antiglomerular basement membrane antibodies in the diagnosis of Goodpasture syndrome: a comparison of different assays. Nephrol Dial Transplant. 2006;21(2):397-401. 6. Borza DB, Chedid MF, Colon S, Lager DJ, Leung N, Fervenza FC. Recurrent Goodpasture’s disease secondary to a monoclonal IgA1-kappa antibody autoreactive with the alpha1/ alpha2 chains of type IV collagen. Am J Kidney Dis. 2005;45(2): 397-406. 7. Maes B, Vanwalleghem J, Kuypers D, Van Damme B, Waer M, Vanrenterghem Y. IgA antiglomerular basement membrane disease associated with bronchial carcinoma and monoclonal gammopathy. Am J Kidney Dis. 1999;33(2):E3. 8. Gandhi S, Little MA, Farrington K. Waldenstrom’s macroglobulinemia presenting as Goodpasture’s syndrome. Ren Fail. 2004;26(5):591-596. 9. Fischer EG, Lager DJ. Anti-glomerular basement membrane glomerulonephritis: a morphologic study of 80 cases. Am J Clin Pathol. 2006;125(3):445-450. 10. Kidney Disease: Improving Global Outcomes (KDIGO) Glomerulonephritis Work Group. KDIGO clinical practice guideline for glomerulonephritis. Kidney Int Suppl. 2012;2:139-274. 11. Wilson CB, Dixon FJ. Anti-glomerular basement membrane antibody-induced glomerulonephritis. Kidney Int. 1973;3(2): 74-89. 12. Hutchison CA, Harding S, Hewins P, et al. Quantitative assessment of serum and urinary polyclonal free light chains in patients with chronic kidney disease. Clin J Am Soc Nephrol. 2008;3(6):1684-1690. 13. Lin J, Markowitz GS, Valeri AM, et al. Renal monoclonal immunoglobulin deposition disease: the disease spectrum. J Am Soc Nephrol. 2001;12(7):1482-1492. 14. Nasr SH, Satoskar A, Markowitz GS, et al. Proliferative glomerulonephritis with monoclonal IgG deposits. J Am Soc Nephrol. 2009;20(9):2055-2064. 15. Noel LH, Aucouturier P, Monteiro RC, Preud’Homme JL, Lesavre P. Glomerular and serum immunoglobulin G subclasses in membranous nephropathy and anti-glomerular basement membrane nephritis. Clin Immunol Immunopathol. 1988;46(2):186194. 16. Qu Z, Cui Z, Liu G, Zhao MH. The distribution of IgG subclass deposition on renal tissues from patients with anti-glomerular basement membrane disease. BMC Immunol. 2013;14:19. 17. Fervenza FC, Terreros D, Boutaud A, et al. Recurrent Goodpasture’s disease due to a monoclonal IgA-kappa circulating antibody. Am J Kidney Dis. 1999;34(3):549-555. 18. Savige JA, Yeung SP, Bierre AR, Kincaid-Smith P. Lambda-light-chain-mediated anti-GBM disease. Nephron. 1989;52(2):144-148. 325
Coley et al 19. de Caestecker MP, Hall CL, MacIver AG. Atypical antiglomerular basement membrane disease associated with thin membrane nephropathy. Nephrol Dial Transplant. 1990;5(11): 909-913. 20. Litwin CM, Mouritsen CL, Wilfahrt PA, Schroder MC, Hill HR. Anti-glomerular basement membrane disease: role of enzyme-linked immunosorbent assays in diagnosis. Biochem Mol Med. 1996;59(1):52-56. 21. Yang R, Hellmark T, Zhao J, et al. Antigen and epitope specificity of anti-glomerular basement membrane antibodies in patients with Goodpasture disease with or without anti-neutrophil cytoplasmic antibodies. J Am Soc Nephrol. 2007;18(4):1338-1343. 22. Salama AD, Dougan T, Levy JB, et al. Goodpasture’s disease in the absence of circulating anti-glomerular basement membrane antibodies as detected by standard techniques. Am J Kidney Dis. 2002;39(6):1162-1167. 23. Cui Z, Zhao MH, Singh AK, Wang HY. Antiglomerular basement membrane disease with normal renal function. Kidney Int. 2007;72(11):1403-1408. 24. Sethi S, Lewin M, Lopez L, Lager D. Linear antiglomerular basement membrane IgG but no glomerular disease: Goodpasture’s syndrome restricted to the lung. Nephrol Dial Transplant. 2007;22(4):1233-1235.
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25. Ohlsson S, Herlitz H, Lundberg S, et al. Circulating antiglomerular basement membrane antibodies with predominance of subclass IgG4 and false-negative immunoassay test results in anti-glomerular basement membrane disease. Am J Kidney Dis. 2014;63(2):289-293. 26. Olaru F, Wang XP, Luo W, et al. Proteolysis breaks tolerance toward intact alpha345(IV) collagen, eliciting novel antiglomerular basement membrane autoantibodies specific for alpha345NC1 hexamers. J Immunol. 2013;190(4):1424-1432. 27. Hellmark T, Segelmark M, Unger C, Burkhardt H, Saus J, Wieslander J. Identification of a clinically relevant immunodominant region of collagen IV in Goodpasture disease. Kidney Int. 1999;55(3):936-944. 28. Cui Z, Wang HY, Zhao MH. Natural autoantibodies against glomerular basement membrane exist in normal human sera. Kidney Int. 2006;69(5):894-899. 29. Knoll G, Rabin E, Burns BF. Antiglomerular basement membrane antibody-mediated nephritis with normal pulmonary and renal function. A case report and review of the literature. Am J Nephrol. 1993;13(6):494-496. 30. Ang C, Savige J, Dawborn J, et al. Anti-glomerular basement membrane (GBM)-antibody-mediated disease with normal renal function. Nephrol Dial Transplant. 1998;13(4):935-939.
Am J Kidney Dis. 2015;65(2):322-326
A
nti–glomerular basement membrane (anti-GBM) disease (also known as Goodpasture syndrome) is an autoimmune disorder that typically presents as pulmonary hemorrhage and rapidly progressive glomerulonephritis. However, milder renal-limited forms of the disease occur.1 The disease is triggered by autoantibodies directed against the “Goodpasture antigen,” the noncollagenous (NC1) domain of the a3 chain of type IV collagen expressed on basement membranes of glomerular and pulmonary capillaries.2,3 Circulating antibodies with specificity for GBM proteins are pathognomonic and detected in more than 97% of patients with anti-GBM disease.4,5 These autoantibodies almost always are polyclonal immunoglobulin G (IgG), with rare reported cases of polyclonal IgA-mediated or monoclonal From the 1Department of Pathology & Cell Biology, Columbia University Medical Center, New York, NY; 2Winthrop University Hospital, Mineola, NY; and 3Department of Medicine, Columbia University Medical Center, New York, NY. Received May 20, 2014. Accepted in revised form August 6, 2014. Originally published online October 21, 2014. Address correspondence to Vivette D. D’Agati, MD, Department of Pathology, Columbia University, College of Physicians and Surgeons, Renal Pathology Laboratory, Rm VC14-224, 630 W 168th St, New York, NY 10032. E-mail: [email protected] 2015 by the National Kidney Foundation, Inc. 0272-6386 http://dx.doi.org/10.1053/j.ajkd.2014.08.022 322
gammopathy–associated anti-GBM disease.6-8 In kidney biopsy specimens, smooth linear staining for IgG is seen exclusively along the GBM, and the most common histologic pattern is severe necrotizing and crescentic glomerulonephritis.9 Treatment involves cyclophosphamide, high-dose corticosteroids, and/or plasmapheresis.10 The prognosis of untreated anti-GBM disease is poor, and kidney survival correlates with the percentage of glomeruli containing crescents.9,10 We report a patient with monoclonal anti-GBM antibody–related glomerulonephritis without a circulating antibody who showed an indolent clinical course.
CASE REPORT A 53-year-old white man was referred to nephrology after developing asymptomatic decreased kidney function following a viral upper respiratory tract infection 4 months prior. He had a history of hypertension and atypical angina and had been taking a statin and verapamil for the 3 years leading up to presentation. He denied hemoptysis, skin rash, or joint pain. Physical examination was unremarkable. Laboratory studies showed the following values: serum creatinine (Scr), 3 mg/dL (corresponding to estimated glomerular filtration rate [eGFR] of 22 mL/min/1.73 m2, as calculated using the isotope-dilution mass spectrometry–traceable 4-variable MDRD [Modification of Diet in Renal Disease] Study equation); albumin, 4.5 g/dL; hemoglobin, 9.9 mg/dL; white blood cell count, 7.8 3 103/mL; and platelet count, 274 3 103/mL. Urine studies revealed microhematuria, and urine protein-creatinine ratio was 689 mg/g. Serologic tests were negative for antinuclear antibody, antineutrophil cytoplasmic antibody, anti-GBM antibody, Am J Kidney Dis. 2015;65(2):322-326
Monoclonal IgG1k anti-GBM Disease
Figure 1. Histologic findings in the initial biopsy and 9-year follow-up biopsy specimens. Light microscopy of the initial kidney biopsy specimen showed (A) diffuse endocapillary proliferative and exudative glomerulonephritis with (B) multifocal GBM breaks (arrows), (C) many glomerular monocytes/macrophages, and (D) focal red blood cell casts. Follow-up kidney biopsy 9 years later also showed (E) diffuse endocapillary proliferative and exudative glomerulonephritis, though now (F) with a single fibrocellular crescent, and (G) severe global glomerulosclerosis and moderate tubulointerstitial scarring. Immunofluorescence micrographs showing monoclonal IgG1k (immunoglobulin G, subclass 1, k light chain) linear staining of glomerular basement membranes ([H] IgG1; [I] IgG2; [J] IgG3; [K] IgG4; [L] k light chain; [M] l light chain). (A, D, E) Hematoxylin and eosin stain, (B, F, G) Jones methenamine silver stain, (C) CD68 immunostain. Original magnification, 3600, except for panel G (3200).
antistreptolysin O antibody, anti–hepatitis B virus, and anti–hepatitis C virus antibodies. There was no hypocomplementemia. Kidney biopsy (Fig 1A-D) showed mild diffuse endocapillary proliferative and exudative glomerulonephritis with many intracapillary monocytes/macrophages and multifocal GBM breaks, focal red blood cell casts, moderate interstitial inflammation and edema, and mild tubulointerstitial scarring. Immunofluorescence microscopy (Fig 1H-M) revealed intense diffuse linear staining of the GBM for IgG and k light chain, with sparse granular staining (trace to 11) of glomerular capillary walls for C3 and no detectable staining for IgM, IgA, C1, and l light chain (Dako). There was no staining detected in Bowman capsule, tubular basement membranes, or vessel walls. Staining for the IgG subclasses (antibodies obtained from The Binding Site) showed restricted positivity for IgG1 with no detectable positivity for IgG2, IgG3 or IgG4 along the GBM (Fig 1H-K). Electron microscopy detected multifocal gaps in the GBM and no electron-dense deposits (Fig 2). Curiously, no crescents or fibrinoid necrosis were seen in more than 20 glomeruli sampled. Following biopsy, serum and urine protein electrophoresis with immunofixation were negative for monoclonal protein. Repeat serologic test results for anti-GBM antibody, antineutrophil cytoplasmic antibody, antinuclear antibody, antistreptolysin O antibody, anti-hepatitis B virus antibody, anti-hepatitis C virus antibody, C3, and C4 were negative or normal. Prednisone (80 mg/d) was given, then the dosage was tapered over 2 months, Am J Kidney Dis. 2015;65(2):322-326
after which the patient’s Scr level peaked at 4 mg/dL (eGFR, 16 mL/min/1.73 m2). Repeat kidney biopsy showed similar histologic findings, and the patient was treated with a 6-month course of intravenous cyclophosphamide (750 mg/m2) and oral prednisone (60 mg/d) and then switched to maintenance monotherapy with mycophenolic acid (720 mg twice daily). He did well for many years, with stable Scr levels of w1.7 mg/dL (eGFR, 42 mL/ min/1.73 m2) and persistent microhematuria and proteinuria (protein excretion quantified at 0.4-1.5 g/d). Because multiple commercially available tests had failed to detect circulating anti-GBM antibody, indirect immunofluorescence was performed by layering the patient’s serum on normal kidney tissue. Again, no anti-GBM antibody was detected, though the false-negative rate for this technique can reach 40%.11 Myeloma workup was negative, including positron emission tomography-computed tomography and bone marrow biopsy. Results from multiple serum free light chain studies showed normal levels of k and l light chains with k:l ratio ranging from 1.11 to 1.82, at times mildly elevated according to the reference range (0.26-1.65). However, the ratio remained within the expected range for patients with decreased kidney function (0.373.1).12 Cryoglobulin studies and serum protein electrophoresis results were repeatedly negative. Nine years after the original episode, the patient again presented with worsening kidney function (Scr, 2.15 mg/dL; eGFR, 31 mL/ min/1.73 m2), proteinuria with protein excretion of 910 mg/d, 323
Coley et al
Figure 2. Electron micrographs show (A) representative gap in glomerular basement membranes plugged by apposition of endothelial cells and podocytes (arrows, initial biopsy; original magnification, 325,000). No immune-type electron-dense deposits were seen in the (B) initial kidney biopsy (original magnification, 350,000) or (C) 9-year follow-up biopsy specimen (original magnification, 310,000).
and hematuria (21 red blood cells/high-power field) after a viral upper respiratory tract infection. The kidney biopsy specimen showed mild diffuse endocapillary proliferative and exudative glomerulonephritis, though this time with a single fibrocellular crescent, severe global glomerulosclerosis, and moderate tubulointerstitial scarring (Fig 1E-G). Again, strong smooth linear and IgG1k (IgG subclass 1, k light chain)–restricted staining of the GBM highlighted focal GBM breaks; no electron-dense deposits were seen (Fig 2C). Repeat testing for anti-GBM antibody (multiplex bead assay) gave negative results. He was treated with 2 doses of rituximab (1 g) separated by 2 weeks. At the time of writing this article, the patient’s Scr level was 1.9 mg/dL (eGFR, 36 mL/min/1.73 m2), urine protein-creatinine ratio was 1.70 mg/g, and urinalysis showed 13 red blood cells/high-power field. He remains on treatment with mycophenolic acid, 720 mg twice daily. Overall, our patient experienced a relatively indolent course of kidney disease punctuated by episodes of increased clinical activity. Kidney biopsy showed some features of anti-GBM nephritis, including linear staining along the GBM and breaks in the GBM, but unusual features of monoclonal staining and mild endocapillary proliferation without fibrinoid necrosis or crescents, except for a single fibrocellular crescent only in the most recent biopsy specimen. Over a 9-year span, glomerulosclerosis and tubulointerstitial scarring increased from 5% to 70% and 10% to 40%, respectively, despite ongoing immunosuppressive therapy.
DISCUSSION Considering the strong monoclonal IgG staining of GBM, the histologic differential diagnosis includes atypical anti-GBM nephritis, light and heavy chain immunoglobulin deposition disease, and proliferative glomerulonephritis with monoclonal immunoglobulin deposits. The absence of linear staining of tubular basement membranes and absence of nodular 324
glomerulosclerosis provided evidence against light and heavy chain immunoglobulin deposition disease.13 Although the monoclonal IgG deposits in proliferative glomerulonephritis with monoclonal immunoglobulin deposits are limited to glomeruli, the absence of glomerular electron-dense deposits ruled out this possibility.14 By exclusion, atypical anti-GBM nephritis was supported by the GBM-restricted linear IgG deposits and multifocal ruptures of the GBM without corresponding electron-dense deposits. Atypical features included the mild endocapillary proliferative pattern without fibrinoid necrosis or crescents, monoclonal nature of the IgG staining, indolent course, and undetectable GBMspecific antibody in the circulation. Passive adsorption of IgG resulting in linear GBM staining without electrondense deposits can be seen with diabetes or monoclonal paraproteinemia, neither of which was detected in our patient. Although we cannot definitively exclude passive adsorption without a positive test for GBM-specific antibody, we believe the atypical findings fit best with a monoclonal form of anti-GBM nephritis. Typically, anti-GBM disease manifests as polyclonal IgG bound to GBM, with studies showing variable results regarding the dominant IgG subtype.4,15,16 Other case reports of monoclonal antibody–associated anti-GBM disease have involved IgA, IgM, or l light chain only.17-19 Our case is the first report of anti-GBM disease with linear GBM staining for monoclonal IgG. Typical screening tests for circulating anti-GBM antibody are based on enzyme-linked immunosorbent Am J Kidney Dis. 2015;65(2):322-326
Monoclonal IgG1k anti-GBM Disease
assay (ELISA) using purified GBM proteins or recombinant Goodpasture antigen, which has reported sensitivity of 65% to 100%.5,20 False-negative results from ELISA testing have been attributed to anti-GBM antibody of low titer or directed toward nonGoodpasture GBM antigens.21,22 Of note, in 3 patients with crescentic anti-GBM disease and negative ELISA results for anti-GBM antibody, a biosensorbased assay was able to detect serum anti-GBM antibody of either low titer and/or low antigen-binding affinity.22 In several reports showing strong linear staining of the GBM but undetectable circulating antiGBM antibody, subsequent alternative serum assays detected an IgG4-predominant polyclonal anti-GBM antibody. This IgG4 predominance often was associated with milder kidney disease.23-26 Low-titer anti-GBM antibody and atypical autoantibody specificity also have been linked with less aggressive disease.27,28 A handful of cases of very mild kidney disease but strong linear GBM staining have been reported.23,26,29,30 Interestingly, one of these cases was associated with an IgG4-predominant autoantibody specific for a quaternary-structure epitope of the NC1 hexamer of a3, a4, and a5 chains of collagen IV and thus could not be detected using tests based on monomeric Goodpasture antigen.26 Our patient likely has a circulating monoclonal IgG1k anti-GBM antibody that we have not yet been able to detect. This antibody may be low titer, have a low rate of synthesis or a high rate of clearance, have low binding affinity, or be directed toward an atypical GBM epitope, explaining the negative results with commercially available screening tests. Alternately, our patient’s monoclonal anti-GBM antibody may be directed toward a private epitope (ie, an epitope unique to his GBM), which would explain the negative results by indirect immunofluorescence staining using his serum on normal kidney tissue. The reason that our patient’s disease course has been relatively indolent compared to the typical rapidly progressive course of anti-GBM disease may be because his monoclonal anti-GBM antibody inefficiently triggers downstream events that mediate the classic necrotizing and crescentic glomerulonephritis such as complement activation or neutrophil participation.11 In summary, we report a unique case of indolent anti-GBM nephritis associated with strong linear monoclonal IgG1k staining of the GBM and to date, no detectable circulating anti-GBM antibody or monoclonal paraprotein.
ACKNOWLEDGEMENTS Support: Dr Coley received fellowship funding supported by the Glomerular Center of Columbia University. Financial Disclosure: The authors declare that they have no relevant financial interests. Am J Kidney Dis. 2015;65(2):322-326
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